Fish should be iced down immediately to help prevent bacterial growth, spoilage – even when the weather is cool.
Fish are easily damaged when improperly handled after landing them in the net. It is important to avoid bruising fish as they are lifted on deck and stowed in the cooler. Bumping and bruising the fish may release enzymes which softens the flesh and makes nutrients available for bacterial growth. Bruises and cuts on the fish are unsightly and provide bacteria access to an otherwise sterile tissue. Research has shown that even unbruised fish flesh taken from bruised fish contain ten times more bacteria than did flesh from unbruised fish resulting in reduced quality and shortened shelf life.
Temperature is the single most important factor affecting the quality of fish as the rate of bacterial growth and spoilage are dependent on it. These processes occur slower as the temperature is lowered. Although it is not possible to completely stop bacterial growth by chilling fish, the rate of bacterial growth and spoilage can be significantly reduced by keeping fish chilled as close to freezing as possible.
Rapid onboard icing is the most effective means of controlling bacteria as it quickly brings the temperature of the fish down to below 40oF. The benefits of icing include rapid cooling of the fish, slows bacterial and enzymatic activity, flushes away bacteria as it melts, prevents drying, delays rigor mortis for improved texture, and resists freezing in cold weather for improved texture. Ice is convenient and inexpensive and its use should not be postponed until arrival at dockside.
Michigan State University in a past study related to the Great Lakes commercial fishing industry demonstrated the importance on onboard icing of fish. Although air and water temperatures were lower in one trial with no ice on board, bacteria and hypozanthine (a product of degradation) increased more rapidly during storage than in another trial when fish were iced on board at higher temperatures. This study supports the recommendation that fish be iced regardless of weather conditions. The study also showed the need for the use of ice even when fish are held at 30o F as the flushing action of melting ice extended shelf life.
When ice is used for cooling and storage it should be placed with the fish to ensure the greatest contact with the fish surfaces. Enough ice should be used so that fish contact only ice as they should not be in contact with each other or the bottom or sides of the cooler. Fish contacting each other or the cooler may promote spoilage by anaerobic bacteria. Flake ice is the best to use as it will not cause bruising of the fish and it provides a better contact area with the surface of the fish.